1. Field of the Disclosure
The disclosure relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a narrow bezel and an increase in brightness and image qualities.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices are most widely used for monitors of notebook computers, monitors of personal computers and televisions due to excellent moving images and high contrast ratio. LCD devices use the optical anisotropy and polarization properties of liquid crystal molecules of a liquid crystal layer to produce an image.
An LCD device includes two substrates spaced apart from and facing each other and a liquid crystal layer interposed between the two substrates. The alignment direction of the liquid crystal molecules is controlled by varying the intensity of an electric field applied to the liquid crystal layer, and the transmittance of light through the liquid crystal layer is changed.
The LCD devices require an additional light source because the LCD devices are not self-luminescent. Therefore, a backlight unit is disposed at a rear side of a liquid crystal (LC) panel and emits light into the LC panel, whereby discernible images can be displayed.
Backlight units include cold cathode fluorescent lamps (CCFLs), external electrode fluorescent lamps (EEFLs), and light emitting diodes (LEDs) as a light source. Among these, LEDs have been widely used due to their small sizes, low power consumption, and high reliability.
Backlight units are in general classified as edge type or direct type according to the position of the light source with respect to a display panel. In edge-type backlight units, one or a pair of lamps are disposed at one side or at each of two sides of a light guide plate of a backlight unit. In direct-type backlight units, a plurality of lamps is disposed directly under the display panel.
The direct-type backlight units have restrictions on decreasing a thickness of an LCD device, and the direct-type backlight units are widely used for LCD devices that focus on brightness rather than a thickness of a screen. The edge-type backlight units can have lighter weights and thinner thicknesses than the direct-type, and the edge-type backlight units are widely used for LCD devices that focus on thicknesses such as monitors of notebook computers or personal computers.
FIG. 1 is a cross-sectional view of illustrating an LCD device including an edge-type backlight unit using LEDs as a light source according to the related art.
In FIG. 1, the related art LCD device includes a liquid crystal panel 10, an edge-type backlight unit 20, a guide panel 30, a top cover 40 and a cover bottom 50.
The liquid crystal panel 10 displays images and includes first and second substrates 12 and 14 facing and attached to each other with a liquid crystal layer (not shown) interposed therebetween.
Polarizers 19a and 19b are attached at front and rear surfaces of the liquid crystal panel 10, respectively, and control the polarization of light.
The backlight unit 20 is disposed at a rear side of the liquid crystal panel 10. The backlight unit 20 includes an LED assembly 29, a reflection sheet 25, a light guide plate 23 and a plurality of optical sheets 21. The LED assembly 29 is disposed at an edge of at least one side of the guide panel 30 along a length direction of the guide panel 30, and includes LEDs 29a and a printed circuit board (PCB) 29b on which the LEDs 29a are mounted. The reflection sheet 25 is disposed over the cover bottom 50 and is white- or silver-colored. The light guide plate 23 is disposed over the reflection sheet 25. The plurality of optical sheets 21 is disposed over the light guide plate 23.
Edges of the liquid crystal panel 10 and the backlight unit 20 are surrounded by the guide panel 30 having a rectangular frame shape. The top cover 40 covers edges of a front surface of the liquid crystal panel 10, and the cover bottom 50 covers a rear surface of the backlight unit 20. The top cover 40 and the cover bottom 50 are combined with the guide panel 30 to thereby constitute one-united body.
Various optical designs are considered to provide a surface light source from the backlight unit 20 of the LCD device to the liquid crystal panel 10. Among these, maintaining an optical gap A between the light guide plate 23 and the LED assembly 29 is a significant factor.
However, when an LCD device having light weight, slim thickness and narrow bezel, which is recently required, is embodied, light leakage may occur because additional elements for preventing movement of the light guide plate 23 are near by an active area where an image is displayed. To prevent the light leakage, the additional elements may be removed, and in this case, it is difficult to maintain the optical gap A between the light guide plate 23 and the LED assembly 29.
Thus, it is not easy to provide high surface light source to the liquid crystal panel 10. In particular, there may occur light leakage between the light guide plate 23 and the LED assembly 29 or the LED assembly may be damaged by movement of the light guide plate 23.
Therefore, problems of lowering qualities of the LCD device such as decreases in brightness and image qualities are caused.